a. Field of the Invention
The present invention relates to a method of developing electrically formed latent images and a developer adoptable for electrophotographic process, electrostatic paper printing process and electrostatic textile printing process for use in forming a multicolor image or a combination of many kinds of color images.
b. Description of the Prior Art
Hitherto, various types of photographic method and printing method have been known and used which comprise the steps of forming an electrical latent image (electrostatic latent image) and making the latent image visible with toner. For example, there are disclosed many electrophotographic methods of this type in U.S. Pat. No. 2,297,691, British Pat. No. 1,165,406 and British Pat. No. 1,165,405 specifications. In these electrophotographic methods, generally using a suitable photoconductive material, an electrical latent image is formed on a photosensitive member by means of various means and then the latent image is developed with toner. The toner image is, if necessary, transferred to a transfer sheet such as paper and fixed with heat, pressure or solvent steam to obtain a copy. To visualize such an electrical latent image with toner, various methods are also known. For example, U.S. Pat. No. 2,874,063 has disclosed the magnetic brush method, U.S. Pat. No. 2,618,552 has disclosed the cascade process and U.S. Pat. No. 2,221,776 has described the powder cloud method.
The methods hitherto proposed and known for producing a multicolor image by electrophotographic process, electrostatic printing process or the like typically comprise the steps of exposing an original utilizing a color filter to divide it into fundamental color components and developing each of the electrostatic latent image thus formed with toners colored in yellow, magenta and cyan or others respectively. By overlapping these developed color components, the neutral tints of the original are reproduced so that an aimed color image may be obtained. In this case, to reproduce all of the colors, only three kinds of toners differently colored as mentioned above or four kinds of toners added by black toner are required.
As other processes which involve the formation of multicolor image or many different colored images, there are known electrophotographic textile printing process and electrostatic textile printing process.
In these textile printing processes, an electrical latent image corresponding to the pattern of original is formed by a suitable method such as electrophotography and electrostatic printing. After developed with printing toner, the image is transferred onto a textile such as cloth and thereafter steaming, soaping and drying are carried out to it so as to pring the color pattern on it.
For such a textile printing according to the electrophotographic method, it is impossible to reproduce any color pattern in neutral tints by employing three or four colored toners as described above. If the above described process is employed to reproduce the multicolor image or the color pattern in neutral tint on a textile, forming of multicolor toner image or neutral color toner image may be possible, but fixing of the neutral color pattern by steaming will become entirely impossible on the textile.
For example, when a green pattern is desired to print on a textile and when a steaming is carried out for the transferred image which has been placed on the textile by transferring firstly a corresponding yellow toner image and secondly cyan toner image overlaid on the former, then it will be found that the color of the pattern really printed on the textile is not green but yellow that is the color of the firstly transferred toner image.
As will be understood from the above example, an ordinary color printing technique as previously mentioned can not be employed in effecting the electrophotographic textile printing process. If a green pattern is desired to print on a textile, a green toner must be used. However, for textile printing, there will be required a large number of different colors. Furthermore even in one color there are extensive varieties in gradation, saturation and the like. Therefore, it is very difficult to prepare and stock all the different color toners as required.
For electrostatic textile printing, another problem arises in printing blended yarn fabrics. Since some different sorts of yarns constitute the fabric and the kind of dyestuff suitable for the yarn is also different depending upon the sort of yarn, all kinds of dyestuffs suitable to all sorts of yarns present in the fabric have to be dispersed in the toners respectively. As there are many kinds of blended yarn fabric and a large number of colors used in printing them, it is again hardly performable to prepare and stock so many different kinds of toners. In addition, mixing and dispersing various dyestuffs into the toners often cause some changes of the toner in chargeability and polarity, which makes the toners useless. Between the electrophotographic textile printing process and the electrophotographic paper printing, there are several differences. This is because in the former some chemical dyeing is carried out after the developed image has been transferred to the textile. For example, for textile printing, the printing color toner must be chemically fixed on the textile and the printed color pattern should have a sharpness, color fastness to washing, color fastness to heat such as ironing and color fastness to light. Furthermore, to dye the textile with dyestuff(s) contained in the toner, the developed image transferred to the textile is subjected to steaming, soaping and drying treatments. After fixing, toner binder resin remained on the textile has to be removed by using some organic solvent. As these facts indicate, the electrophotographic printing process differs from the conventional electrophotographic process where the developed image is transferred to a paper and then fixed.